How is the efficiency of read operations in a hash table evaluated?

The efficiency of read operations in a hash table is usually evaluated based on the average access time to an element — it tends to approach O(1), meaning constant time.

This is achieved by computing a hash function for the key, which determines the index in the array where the value is stored. With a good hash function and low collision rate, the search is very fast.

However, in the worst case, when there are many collisions, read operations can degrade to O(n) if all elements end up in the same bucket.

To assess efficiency, the following are usually considered:

• Average access time (amortized)
• Number of collisions
• Load factor of the table

Example: in C++, the standard std::unordered_map provides an average access time of O(1), but it can slow down with high load factor.